In the production of welded pipes with used high frequency tube mills, the manifestations of cracks include long cracks, partial periodic cracks, and irregular intermittent cracks. Some steel pipes have no cracks on the surface after welding, but cracks appear after flattening, straightening or water pressure tests.

There are three main reasons that affect the cracks in the production of used high frequency tube mills: ①The quality of raw materials is poor. ②Edge joint state. ③The selection of process parameters is unreasonable. We explain and prevent the influencing factors of poor quality of raw materials and the state of edge joints.

① Poor quality of raw materials

In the production of welded pipes, large edge burrs and excessive width of the raw material are often problems.

If the burr is outwards during welding, it is easy to produce continuous and long intermittent cracks;

The width of the raw material is too wide, and the squeeze roll pass is over-filled, forming a welded peach shape, with large outer weld scars, small or no inner weld ribs, and cracks after straightening.

②Edge joint state

The fillet joint state of the edge of the tube blank is a common phenomenon in the production of welded pipes. The smaller the pipe diameter, the more serious the fillet joint.

Inadequate forming adjustment is a prerequisite for corner joints.

The improper design of the squeeze roller pass, the large outer corner of the pass, and the elevation angle of the squeeze roller adjustment are the key factors that affect the corner joint.

The single-radius squeeze roll pass cannot eliminate the corner joint problems caused by poor forming. Increase the squeezing force, or the squeeze roll pass wears in the later stage of production and becomes a vertical oval, which intensifies the sharp peach-shaped welding state. Severe corner joints occur.

The corner joint will cause most of the metal to flow out from the upper side, forming an unstable melting process. At this time, there will be large metal splashes, overheated weld joints, and external burrs that are hot, irregular, large and not easy to scratch If the welding speed is slightly improperly controlled, the "false welding" of the weld will inevitably occur.

The outer corner of the squeeze roller is large, which makes the tube blank insufficiently filled in the squeeze roller, and the edge contact state changes from parallel to a "V" shape, and there is a phenomenon that the inner weld is not welded.

The squeeze roller shaft is stressed and worn for a long time, and the base bearing is worn, and the two shafts form an elevation angle, resulting in insufficient squeezing force, vertical ellipse and serious angle joint.

The factors that affect the production of longitudinal welded pipes with used high frequency tube mills are to be prevented according to the actual situation to prevent weld cracks during the production of longitudinal welded pipes.